The present invention relates to a radiation image storage panel employed in a radiation image recording and reproducing method utilizing a double-side reading system.
As a method replacing a conventional radiography, a radiation image recording and reproducing method utilizing a stimulable phosphor was proposed, and is practically employed. The method employs a radiation image storage panel (i.e., stimulable phosphor sheet) comprising a stimulable phosphor, and comprises the steps of causing the stimulable phosphor of the storage panel to absorb radiation energy having passed through an object or having radiated from an object; sequentially exciting the stimulable phosphor with an electromagnetic wave such as visible light or infrared rays (i.e., stimulating light) to release the radiation energy stored in the phosphor as light emission (i.e., stimulated emission); photoelectrically detecting the emitted light to obtain electric signals; and reproducing the radiation image of the object as a visible image from the electric signals. The panel thus treated is subjected to a step for erasing a radiation image remaining therein, and then stored for the next recording and reproducing procedure. Thus, the radiation image storage panel can be repeatedly employed.
In this method, a radiation image is obtainable with a sufficient amount of information by applying a radiation to the object at a considerably smaller dose, as compared with a conventional radiography using a combination of a radiographic film and radiographic intensifying screen.
The radiation image storage panel has a basic structure comprising a support and a stimulable phosphor layer provided thereon. However, if the phosphor layer is self-supporting, the support may be omitted. On the free surface (surface not facing the support) of the phosphor layer, a transparent protective film is generally placed to keep the phosphor layer from chemical deterioration or physical damage.
The phosphor layer usually comprises a binder and stimulable phosphor particles dispersed therein, but it may consist of agglomerated phosphor without binder. The phosphor layer containing no binder can be formed by deposition process or firing process. Further, the layer comprising agglomerated phosphor soaked with a polymer is also known. In any types of phosphor layers, the stimulable phosphor emits stimulated emission when excited with a stimulating light after having been exposed to a radiation such as X-rays. Accordingly, the radiation having passed through an object or radiated from an object is absorbed by the phosphor layer of the storage panel in proportion to the applied radiation dose, and a radiation image of the object is produced in the storage panel in the form of a latent radiation energy-stored image. The latent radiation energy-stored image can be released as stimulated emission by sequentially irradiating the panel with stimulating rays. The stimulated emission is then photoelectrically detected to give electric signals, so as to reproduce a visible image from the electric signals.
The radiation image recorded in the storage panel is generally read by the steps of applying a stimulating light to the front surface side (the phosphor layer side or the protective film side) of the storage panel, collecting light emitted by the phosphor particles by means of a light-collecting means from the same side, and photoelectrically converting the emitted light into digital signals corresponding to the radiation image. A system for reading the radiation image from one side of the storage panel in this manner is referred to as xe2x80x9csingle-side reading systemxe2x80x9d. However, there is a case that the light emitted by the phosphor particles should be collected from both sides (i.e., the front and the back surface sides) of the storage panel. For instance, there is a case that the emitted light is desired to be collected as much as possible. There is also a case that the radiation image recorded in the phosphor layer varies along the depth of the phosphor layer, and that the variation is desired to be detected. A system for reading the image from both sides of the panel is referred to as xe2x80x9cdouble-side reading systemxe2x80x9d.
A radiation image storage panel employed in the double-side reading system, as well as a panel employed in the single-side reading system, is desired to be as sensitive as possible and to provide an image of high quality (high sharpness, high resolution, high graininess, etc.).
Generally, in a radiation image storage panel for the double-side reading system, the amount of the stimulated emission detected from the back surface side is considerably small as compared with that from the front surface side. Accordingly, the radiation image obtained from the back surface side is liable to have poor quality. The reason why the emission is detected from the back surface side in a less amount is thought to be as follows.
The stimulating light is applied onto only the front surface side of the panel (i.e., only the top surface side of the phosphor layer or the protective layer), and hence it insufficiently reaches phosphor particles near the bottom surface of the phosphor layer. In addition, since a transparent support is generally provided on the back (bottom) surface side of the panel, the emission taken from the support side is often weakened by the support.
For improving the image quality such as sharpness, it is desired to increase the amount of the stimulated emission detected from the back surface side.
It is an object of the present invention to provide a radiation image storage panel giving a radiation image of high quality which is employed in a radiation image recording and reproducing method utilizing a double-side reading system.
The inventors have studied about the aforementioned problems of a radiation image storage panel for a radiation image recording and reproducing method utilizing double-side reading system, and finally found the following facts.
The phosphor layer having an optical transmittance varying along the depth of the phosphor layer gives a radiation image with a high resolution (particularly in a low frequency region). If the transmittance in a part near the bottom surface of the phosphor layer is larger or higher than that in a part near the top surface, the stimulating light reaching the bottom part can be efficiently used and the emission radiating from the bottom surface can be effectively detected. Consequently, the quality of the radiation image obtained from the back surface side can be remarkably improved.
Otherwise, the stimulable phosphor layer of the radiation image storage panel to be used, specifically, in the double-side reading system preferably has a total optical transmittance of 2 to 20% at the maximum peak wavelength of the stimulation spectrum of the stimulable phosphor of the phosphor layer.
The present invention resides in a radiation image storage panel (Radiation Image Storage Panel-I) having a stimulable phosphor layer which is used in a radiation image recording and reproducing method comprising applying a stimulating light to one surface side (i.e., top surface side) of the phosphor layer and collecting stimulated emission from the phosphor layer on both surface sides (i.e., top surface side and bottom surface side), wherein the phosphor layer has an optical transmittance varying along depth of the phosphor layer at each of wavelengths of the stimulating light and the stimulated emission.
The invention also resides in a radiation image recording and reproducing method (Radiation Image Recording and Reproducing Method) which comprises the steps of:
irradiating one surface of a radiation image storage panel with radiation having passed through an object or having been emitted by an object to record a radiation energy image of the object on the radiation image storage panel having a stimulable phosphor layer that has an optical transmittance varying along depth of the phosphor layer at each of wavelengths of stimulating light and stimulated emission;
sequentially exciting the radiation image storage panel by applying the stimulating light to one surface of the storage panel to release the radiation energy recorded in the phosphor layer as the stimulated emission;
photoelectrically detecting the stimulated emission from the excited surface and the opposite surface of the storage panel to obtain electric signals; and
reproducing the radiation image of the object as a visible image from the electric signals.
The invention further resides in a radiation image storage panel (Radiation Image Storage Panel-II) comprising a transparent support film, a stimulable phosphor layer, and a transparent protective film, which is used in a radiation image recording and reproducing method comprising applying a stimulating light to one surface side of the phosphor layer and collecting stimulated emission from the phosphor layer on both surface sides, wherein the phosphor layer has a total optical transmittance in the range of 2 to 20% at a peak wavelength of a stimulation spectrum of the stimulable phosphor. The total optical transmittance includes an optical transmittance by way of diffusion transmission.
The invention furthermore resides in a radiation image storage panel (Radiation Image Storage Panel-III) comprising a transparent support film, a stimulable phosphor layer, and a transparent protective film, which is used in a radiation image recording and reproducing method comprising applying a stimulating light to one surface side of the phosphor layer and collecting stimulated emission from the phosphor layer on both surface sides, wherein the phosphor layer has an optical transmittance in the range of 2 to 20% at a peak wavelength of a stimulated emission spectrum of the stimulable phosphor.
The invention furthermore resides in a method for reading a radiation image storage panel (Radiation Image Reading Method) which comprises the steps of:
applying a stimulating light to a radiation image storage panel comprising a transparent support film, a stimulable phosphor layer, and a transparent protective film, said phosphor layer having an optical transmittance in the range of 2 to 20% at a peak wavelength of a stimulation spectrum of the stimulable phosphor and containing a radiation energy, said stimulating light having a wavelength within xc2x120% of the maximum peak wavelength of the stimulation spectrum of the stimulable phosphor, through the transparent protective film, to release the radiation energy contained in the phosphor layer as stimulated emission;
collecting the stimulating emission from both surface sides of the storage panel; and
photoelectrically converting the collected emission to digital signals.